Detector, power transmitter, power receiver, power feed system, and detection method

ABSTRACT

There are provided a detector and the like that are capable of conveniently detecting conductor or a circuit including a coil. The detector includes a detecting section that determines a Q value or a degree of variation thereof in a circuit including a coil capable of electromagnetic coupling with an external object and that performs detection concerning a state of the electromagnetic coupling with the external object based on a determined result.

TECHNICAL FIELD

The present disclosure relates to a detector and a detection method fordetecting the presence of a conductor such as a metal, or a circuitincluding a coil, as well as a power transmitter, a power receiver, anda power feed system that are provided with such a detector (detectingsection).

BACKGROUND ART

In a noncontact power transmission (noncontact power feed system), it iscritically important in ensuring the safety and performing electricalcharging to detect a conductor such as a metal, or a circuit including acoil that is present in the vicinity of power transmitting and receivingcoils.

Typically, by combined use of a power transmitter and a power receiver,a metallic object that is inserted between the power transmitter(primary-side coil) and the power receiver (secondary-side coil) hasbeen detected based on information on an amplitude and a phase in theevent of variation in the load of the power receiver (for example, seePatent Literature 1). Alternatively, a metallic object has been detectedfrom variation in the transmitting and receiving power efficiency (alsocalled the inter-coil efficiency), or from variation in the sensoroutput by the use of a magnetic sensor, a capacitive sensor, an infraredsensor, or the like.

PRIOR ART DOCUMENT Patent Literature

-   Patent Literature 1: Japanese Patent No. 4413236 (Japanese    Unexamined Patent Application Publication No. 2008-206231)

SUMMARY OF INVENTION

Meanwhile, in such a noncontact power feed system, it is desirable toconveniently detect the above-described conductor (including asemiconductor) such as a metal, or the above-described circuit includinga coil.

The present disclosure has been made in view of such disadvantages, andit is an object of the present disclosure to provide a detector, a powertransmitter, a power receiver, a power feed system, and a detectionmethod that are capable of conveniently detecting a conductor or acircuit including a coil.

A detector according to an embodiment of the present disclosure includesa detecting section that determines a Q value or a degree of variationthereof in a circuit including a coil capable of electromagneticcoupling with an external object and that performs detection concerninga state of the electromagnetic coupling with the external object basedon a determined result.

A power transmitter according to an embodiment of the present disclosureincludes: a power transmitting coil capable of electromagnetic couplingwith an external object; a power transmitting section performing powertransmission using the power transmitting coil; and a detecting sectionthat determines a Q value or a degree of variation thereof in a circuitincluding the power transmitting coil and that performs detectionconcerning a state of the electromagnetic coupling with the externalobject based on a determined result.

A power receiver according to an embodiment of the present disclosureincludes: a power receiving coil capable of electromagnetic couplingwith an external object; a power receiving section performing powerreception using the power receiving coil; and a detecting section thatdetermines a Q value or a degree of variation thereof in a circuitincluding the power receiving coil and that performs detectionconcerning a state of the electromagnetic coupling with the externalobject based on a determined result.

A power feed system according to an embodiment of the present disclosureincludes: one or a plurality of power receivers; and one or a pluralityof power transmitters that perform power transmission utilizing theelectromagnetic coupling for the one or the plurality of powerreceivers. The power transmitter has a power transmitting coil capableof electromagnetic coupling with an external object, and a powertransmitting section to perform power transmission using the powertransmitting coil. The power receiver has a power receiving coil capableof electromagnetic coupling with an external object, and a powerreceiving section performing power reception using the power receivingcoil. A detecting section that determines a Q value or a degree ofvariation thereof in a circuit including the power transmitting coil orthe power receiving coil and that performs detection concerning a stateof the electromagnetic coupling with the external object based on adetermined result is provided at the power transmitter or the powerreceiver or both.

A detection method according to an embodiment of the present disclosureincludes: a first step of determining a Q value or a degree of variationthereof in a circuit including a coil capable of electromagneticcoupling with an external object; and a second step of performingdetection concerning a state of the electromagnetic coupling with theexternal object based on a result determined in the first step.

In the detector, the power transmitter, the power receiver, the powerfeed system, and the detection method according to the above-describedrespective embodiments of the present disclosure, a Q value or a degreeof variation thereof in a circuit including a coil capable ofelectromagnetic coupling with an external object (for example, the powertransmitting coil or the power receiving coil) is determined, anddetection concerning a state of the electromagnetic coupling with theexternal object is performed based on the determined result. This makesit possible to detect a conductor such as a metal, or a circuitincluding an electromagnetically coupled coil without the necessity fora combined use of a primary side (power transmitting side) and asecondary side (power receiving side).

In the detector, the power transmitter, the power receiver, the powerfeed system, and the detection method according to the above-describedrespective embodiments of the present disclosure, it is possible todetect a conductor (including a semiconductor) such as a metal or acircuit including a coil without the necessity for a combined use of aprimary side (power transmitting side) and a secondary side (powerreceiving side). Accordingly, this allows a conductor or a circuitincluding a coil to be detected conveniently.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory circuit diagram showing an overview of anoncontact power transmission system according to a first embodiment ofthe present disclosure.

FIG. 2 is a schematic block diagram showing a configuration example of adetector (detecting circuit) that is provided at a power transmitteraccording to the first embodiment of the present disclosure.

FIG. 3 is a flowchart showing detection processing according to thefirst embodiment of the present disclosure.

FIGS. 4(a) and 4(b) are each a circuit diagram showing another example(parallel resonant circuit) of a resonant circuit.

FIG. 5 is an explanatory schematic diagram showing a method of detectinga conductor.

FIG. 6 is a simplified schematic diagram showing an example of a coil inuse for a power transmitter and a power receiver.

FIG. 7 is a graph showing the characteristics of Q values versus metalsizes (square sizes).

FIG. 8 is an explanatory schematic diagram showing a method of detectinga circuit including a coil.

FIG. 9 is a graph showing the characteristics of a Q value of a resonantcircuit at a power transmitting side versus a load resistance of aresonant circuit at a power receiving side.

FIG. 10 is a schematic cross-sectional view showing a state where ametallic object is interposed between a power transmitting coil and apower receiving coil.

FIG. 11 is a graph showing the various characteristics versus metalsizes (square sizes).

FIG. 12 is a graph showing the frequency characteristics of impedance ina series resonant circuit according to a second embodiment of thepresent disclosure.

FIG. 13 is a graph showing the frequency characteristics of impedance ina parallel resonant circuit according to the second embodiment of thepresent disclosure.

FIG. 14 is a circuit diagram for calculating a Q value from a ratio of areal part component to an imaginary part component of impedanceaccording to a third embodiment of the present disclosure.

DESCRIPTION OF EMBODIMENTS

Hereinafter, some embodiments of the present disclosure are describedwith reference to the attached drawings. The descriptions are providedin the order given below. It is to be noted that any component partswhich are used in common in each figure are denoted with the samereference numerals, and the redundant descriptions are omitted asappropriate.

-   1. First Embodiment (arithmetic processing section: an example of    calculation of a Q value from a ratio of a voltage across a coil to    an L-C voltage in a series resonant circuit)-   2. Second Embodiment (arithmetic processing section: an example of    calculation of a Q value using a half-value width method)-   3. Third Embodiment (arithmetic processing section: an example of    calculation of a Q value from a ratio of a real part component to an    imaginary part component of impedance)-   4. Others (various modification examples)

1. First Embodiment

(Description of Noncontact Power Transmission System)

In a first embodiment of the present disclosure (hereinafter alsoreferred to as “the present embodiment”), the description is provided ona configuration and a method for detecting, with use of a powertransmitter or a power receiver in a noncontact power transmissionsystem (noncontact power feed system), a conductor such as a metal, or acircuit including a coil that may be present in the vicinity of thepower transmitter or the power receiver. Hereinafter, to detect aconductor such as a metal, or a circuit including a coil may be alsotermed “to detect a conductor and the like”. It is to be noted that aconductor mentioned in the present specification encompasses abroadly-defined conductor, that is, a semiconductor.

In the first embodiment, a variation in a Q value representing arelationship of conservation and loss of energy (indicating a resonantintensity of a resonant circuit) in a power transmitter (primary side)or a power receiver (secondary side) is used to detect a conductor andthe like. For example, if a metallic object is present in the vicinityof a power transmitting coil of a power transmitter or a power receivingcoil of a power receiver, a line of magnetic force passes through themetallic object, causing an eddy current to be generated on the metallicobject. Seen from a coil, this seems to be a an electromagnetic couplingof the metallic object and the coil that applies a real resistance loadto the coil, leading to variation in a Q value of the coil. By measuringsuch a variation in the Q value, any metallic object (an electromagneticcoupling state) that may be present in the vicinity of the coil isdetected. The electromagnetic coupling, which may be also called“electromagnetic field resonant coupling” or “electromagneticresonance”, includes an electric field coupling and a magnetic fieldcoupling. Both of the couplings utilize the resonance to perform powertransmission through the electric field coupling or the magnetic fieldcoupling with only a resonating device. However, the electromagneticcoupling (electric field coupling or magnetic field coupling) usingelectromagnetic induction may be performed as an alternative to such aresonance.

FIG. 1 is an explanatory circuit diagram showing an overview of anoncontact power transmission system according to the first embodimentof the present disclosure. FIG. 1 shows an example of the most basiccircuit configuration (in the case of the magnetic field coupling) forthe noncontact power transmission system.

The noncontact power supply system (noncontact power feed system)according to the present embodiment is composed of one or a plurality ofpower transmitters 1 (one in the figure) and one or a plurality of powerreceivers 11 (one in the figure).

The power transmitter 1 carries out the noncontact power transmissionutilizing the electromagnetic coupling for the power receiver 11. Thepower transmitter 1 is provided with a signal source 2 including analternating-current power source 3 for generating an alternating-currentsignal and a resistor element 4; a capacitor 5; and a power transmittingcoil (primary-side coil) 6 that is capable of electromagnetic couplingwith an external object. The resistor element 4 gives a graphicrepresentation of an internal resistance (output impedance) of thealternating-current power source 3. The capacitor 5 and the powertransmitting coil 6 (an example of a coil) are connected with the signalsource 2 in a manner of forming a series resonant circuit (an example ofa resonant circuit). Further, a capacitance value (C value) of thecapacitor 5 and an inductance value (L value) of the power transmittingcoil 6 are adjusted to achieve the resonance at desired measurementfrequency. A power transmitting section 7 that is composed of the signalsource 2 and the capacitor 5 carries out the noncontact powertransmission (electric power transmission (power feed)) to an externalobject through the power transmitting coil 6. In other words, the powertransmitting section 7 is intended to perform the power transmissionusing the power transmitting coil 6.

The power receiver 11 receives a power transmitted in a noncontactmanner from the power transmitter 1 utilizing the electromagneticcoupling. The power receiver 11 is provided with a charging section 12including a capacitor 13 (secondary battery) and a resistor element 14;a rectifying section 18 converting an alternating-current signal into adirect-current signal; a capacitor 15; and a power receiving coil(secondary-side coil) 16 that is capable of electromagnetic couplingwith an external object. The resistor element 14 gives a graphicrepresentation of an internal resistance (output impedance) of thecapacitor 13. The capacitor 15 and the power receiving coil 16 areconnected with the charging section 12 in a manner of forming a seriesresonant circuit, and a capacitance value (C value) of the capacitor 15and an inductance value (L value) of the power receiving coil 16 areadjusted to achieve the resonance at desired measurement frequency. Apower receiving section 17 that is composed of the charging section 12,the rectifying section 18, and the capacitor 15 receives a powertransmitted in a noncontact manner from an external object through thepower receiving coil 16 (performs the power reception). In other words,this power receiving section 17 is intended to perform the powerreception using the power receiving coil 16.

Given that a voltage between the power transmitting coil 6 and thecapacitor 5 that compose a series resonant circuit is V1 (first voltage:an example of a voltage to be applied to a resonant circuit), and avoltage across the power transmitting coil 6 is V2 (second voltage), a Qvalue of the series resonant circuit is represented by Expression 1.

$\begin{matrix}{Q = {\frac{V\; 2}{V\; 1} = \frac{2\pi\;{fL}}{r_{s}}}} & \left\lbrack {{Math}.\mspace{14mu} 1} \right\rbrack\end{matrix}$rs: effective resistance at frequency f.

The voltage V2 is obtained by multiplying the voltage V1 by a Q value.As a metallic object comes closer to the power transmitting coil 6, aneffective resistance rs becomes greater, leading to a decrease in a Qvalue. In such a manner, as a metallic object comes closer to the powertransmitting coil 6, a Q value (electromagnetic coupling state) to bemeasured varies, and thus detection of this variation makes it possibleto detect a metallic object that may be present in the vicinity of thepower transmitting coil 6.

It is to be noted that FIG. 1 shows a basic circuit including a seriesresonant circuit, and thus various forms may be possible as a detailedconfiguration given that the above-described circuit functions areprovided. For example, although FIG. 1 shows the capacitor 13 as anexample of a load to be provided at the power receiver 11, aconfiguration is not limited to the example. Alternatively, aconfiguration where the power receiver 11 has the signal source 2 (powertransmitting section 7) to transmit a power in a noncontact manner to anexternal object via the power receiving coil 16, or a configurationwhere the power transmitter 1 is provided with a load to receive a powerin a noncontact manner from an external object via the powertransmitting coil 6 may be also permitted.

(Description of Detecting Circuit)

FIG. 2 is a schematic block diagram showing a configuration example of adetector (detecting circuit) that is provided at the power transmitteraccording to the first embodiment of the present disclosure. Thedetecting circuit detects a conductor such as a metal, or a circuitincluding a coil. The power transmitter that is provided with thedetecting circuit (detector) corresponds to a specific but notlimitative example of a detector (electromagnetic coupling statedetector).

A detecting circuit 20 according to the present embodiment, whichcorresponds to a specific but not limitative example of a detectingsection (detector), includes rectifying sections 21A and 21B, ananalog-to-digital converter (hereinafter referred to as an “ADC”) 22,and a main control section 23. As described in details hereinafter, thedetecting circuit 20 determines a Q value or a degree of variation inthe Q value in a circuit including a coil (power transmitting coil 6 inthis example) that is capable of electromagnetic coupling with anexternal object, while performing detection concerning a state of theelectromagnetic coupling with the external object based on a determinedresult. As will hereinafter be described in details, in concrete terms,the detecting circuit 20 detects whether or not any other conductor(including a semiconductor) such as a metal, or any other circuitincluding a coil (power receiving coil 16 in this example) may bepresent in the vicinity of a coil (power transmitting coil 6 in thisexample) as a state of the electromagnetic coupling with an externalobject. In addition, when the presence of such a conductor or any othercircuit in the vicinity of the power transmitting coil 6 is detected,the detecting circuit 20 also has a capability to further detect whethera detected object is either a conductor or any other circuit.

The rectifying section 21A converts an alternating-current signal(alternating-current voltage) input from between the power transmittingcoil 6 and the capacitor 5 into a direct-current signal (direct-currentvoltage) to provide such a resultant signal as an output. Similarly, therectifying section 21B converts an alternating-current signal(alternating-current voltage) input from between the signal source 2 andthe capacitor 5 into a direct-current signal (direct-current voltage) toprovide such a resultant signal to the ADC 22 as an output.

The ADC 22 converts analog direct-current signals input from therectifying sections 21A and 21B into digital direct-current signals tooutput such resultant signals to the main control section 23.

The main control section 23, which corresponds to a specific but notlimitative example of a control section, may be composed of, forexample, an MPU (Micro-Processing Unit) to control the overall powertransmitter 1. The main control section 23 includes a functionality asan arithmetic processing section 23A and a determination section 23B.

The arithmetic processing section 23A, which is a block to carry out apredetermined arithmetic processing, in the present embodiment,calculates a ratio of the voltage V1 to the voltage V2, that is, a Qvalue from a direct-current signal incoming from the ADC 22 to output acalculation result to the determination section 23B. More specifically,the arithmetic processing section 23A determines a Q value in a resonantcircuit based on a ratio of the voltage V1 between the powertransmitting coil 6 and the capacitor 5 in the resonant circuit to thevoltage V2 across the power transmitting coil 6 in the resonant circuit.In such a manner, the arithmetic processing section 23A has afunctionality to determine a Q value or a degree of variation thereof.

The determination section 23B compares a calculation result incomingfrom the determination section 23B with a threshold stored on anonvolatile memory 24 to determine whether or not a conductor such as ametal, or a circuit including a coil may be present in the vicinitybased on a comparison result. In other words, the determination section23B has a functionality to determine a state of the electromagneticcoupling with an external object by comparing a Q value or a degree ofvariation thereof that is calculated by the arithmetic processingsection 23A with a predetermined threshold. Hereupon, a threshold for aQ value (Ref_Q1) in a state where nothing is present in the vicinity ofthe power transmitting coil 6, or nothing is placed on the powertransmitting coil 6 has been measured beforehand, and this threshold hasbeen stored in the memory 24. Specifically, the threshold (Ref_Q1)corresponds to a Q value in a resonant circuit under a condition that aconductor and a circuit (any other circuit) including another coil isnot present in the vicinity of the power transmitting coil 6.

A communication control section 25 controls generation of analternating-current voltage by the signal source 2 (power transmittingsection 7) in response to a control signal from the main control section23, thereby allowing the power transmitter 1 to perform the noncontactpower transmission or communication with an external object.

An input section 26 generates an input signal according to a useroperation to output such a resultant signal to the main control section23.

It is to be noted that, in the present embodiment, although aconfiguration where the detecting circuit (detector) is built into thepower transmitter is employed, the detecting circuit (detector) may beprovided in either the power transmitter or the power receiver, or both.In other words, such a detector (detecting section) may be provided inthe power transmitter or the power receiver or both.

With reference to a flowchart shown in FIG. 3, the description isprovided on a detection process (electromagnetic coupling statedetection process) that is carried out by the detecting circuit 20.

The main control section 23 on the detecting circuit 20 carries out ameasurement process of a Q value in a series resonant circuit on aperiodic basis, and determines whether or not a measurement of the Qvalue is made (step S1). The process proceeds to a step S2 when ameasurement is made, and a determination process in the step S1 isrepeated when no measurement is made. It is to be noted that, asdescribed previously, a measurement of the Q value is made using thevoltages V1 and V2 that are obtained through analog-to-digitalconversion by the ADC 22 following the rectification by the rectifyingsections 21A and 21B. The arithmetic processing section 23A calculates aratio of the voltage V1 to the voltage V2 (Q value) to output thecalculated value to the determination section 23B.

It is to be noted that the main control section 23 may perform ameasurement process of the Q value by detecting an input signalincluding instruction information on a measurement of the Q value fromthe input section 26.

Next, the determination section 23B compares the measured Q value withthe threshold for the Q value (Ref_Q1) in a state where nothing ispresent in the vicinity of the power transmitting coil 6, or nothing isplaced on the power transmitting coil 6 to determine whether or not themeasured Q value is within a range of the threshold (Ref_Q1) (step S2).

Here, if the measured Q value is within a range of the threshold(Ref_Q1), the determination section 23B determines that a conductor suchas a metal, or a circuit including a coil is not present in the vicinity(step S3), and the process returns back to the step S1.

On the other hand, if the measured Q value is not within a range of thethreshold (Ref_Q1), the determination section 23B determines that aconductor such as a metal, or a circuit including a coil is present inthe vicinity (step S4), and the process proceeds to a step S5.

Here, if the presence of a conductor or a circuit (any other circuit)including a coil in the vicinity of the power transmitting coil 6 isdetected, the determination section 23B determines whether or not thepower transmitter 1 is capable of communicating with an external object(step S5). In concrete terms, the determination section 23B instructsthe communication control section 25 to perform communication with anexternal object. The communication control section 25 attemptscommunication with an external object by making the signal source 2(power transmitting section 7) generate an alternating-current voltageand by sending out a radio signal (transmission signal) from the powertransmitter 1 (power transmitting coil 6) to the external object.Subsequently, the communication control section 25 determines whether ornot communication with the external object is possible depending on thepresence or absence of a response to the transmission signal.

More specifically, if there is a response from the external object tothe transmission signal from the power transmitter 1 (a response isreturned back), the determination section 23B determines thatcommunication with the external object is possible, and decides that acircuit including a coil is present in the vicinity (step S6). On thecontrary, if there is no response from the external object to thetransmission signal from the power transmitter 1, the determinationsection 23B determines that communication with the external object isnot possible (unfeasible), and decides that a conductor such as a metalis present in the vicinity (step S7).

In such a manner, the determination section 23B determines that adetected object is either a conductor or any other circuit (circuitincluding any other coil) based on a result of determining whether ornot communication with the external object via the power transmittingcoil 6 is possible. In concrete terms, when it is determined thatcommunication with the external object is possible, the determinationsection 23B decides that the detected object is any other circuit, andwhen it is determined that communication with the external object is notpossible, the determination section 23B decides that the detected objectis a conductor.

It is to be noted that, in the present embodiment, although thedescription is provided on an application example where the detectingcircuit 20 is connected with a series resonant circuit, a parallelresonant circuit may be alternatively used as a resonant circuit. Eachof FIGS. 4(a) and 4(b) shows an example of the parallel resonantcircuit. In an example in FIG. 4(a), the parallel resonant circuit isconfigured in such a manner that a capacitor 5A is connected in serieswith a parallel circuit of a capacitor 5B and the power transmittingcoil 6. Further, in an example in FIG. 4(b), the parallel resonantcircuit is configured in such a manner that the capacitor 5B isconnected in parallel with a series circuit of the capacitor 5A and thepower transmitting coil 6. The detecting circuit 20 calculates a Q valueutilizing the voltage V1 between the power transmitting coil 6 and thecapacitor 5A as well as the voltage V2 across the power transmittingcoil 6 that are obtained in the parallel resonant circuit illustrated ineach of FIGS. 4(a) and 4(b). The above-described series resonant circuitand parallel resonant circuit are illustrated by an example for thepurpose of explaining a principle of the detection method(electromagnetic coupling state detection method) according to theembodiment of the present disclosure, and a configuration of theresonant circuit is not limited to these examples.

(Measurement Results)

Next, the description is provided on measurement results of a Q value ina case where a metallic object is actually placed in the vicinity of thepower transmitting coil 6 on the power transmitter 1.

As shown in FIG. 5, a measurement was made in such a manner that thedetecting circuit 20 was operated with a metallic object 31 broughtclose to the power transmitter 1 that was mounted on a pedestal 30.Further, in the measurement, as the power transmitting coil 6, a spiralcoil with a size of 150 mm (W1)*190 mm (W2) which is wound around usinga litz wire 41 (wire diameter ϕ: 1.0 mm) that is a conductor wire with aplurality of narrow copper wires twisted as illustrated in FIG. 6 wasused. Additionally, a magnetic material 42 made of a ferrite materialwith a thickness of 1.0 mm is laid against a backside of the spiralcoil. An L value and a Q value of the power transmitting coil 6 when themetallic object 31 is not present in the vicinity are 192.0 μH and230.7, respectively. A C value of the capacitor 5 to be resonated is 8.2nF. In this case, a resonant frequency of the series resonant circuitincluding the power transmitting coil 6 becomes 127.0 kHz.

Further, given that the Q value of a capacitor is Qc, and the Q value ofa coil is QL, the Q value of the resonant circuit is typicallyrepresented by a relationship of 1/{(1/Qc)+(1/QL)}. The Q value of thecapacitor 5 that was used for the measurement is designed to besufficiently high relative to the Q value of the power transmitting coil6, and thus any effect on the Q value of the series resonant circuit maybe negligible. However, on the contrary, the Q value of the powertransmitting coil 6 may be designed to be sufficiently high relative tothe Q value of the capacitor 5, or both of the power transmitting coil 6and the capacitor 5 may have the nearly equivalent Q values.

An iron (Fe) material and an aluminum (Al) material each having athickness of 1.0 mm are brought close to the series resonant circuitincluding the power transmitting coil 6. A distance between the powertransmitting coil 6 and each of the metallic objects is fixed to 8 mm.Subsequently, the Q values are measured using the detecting circuit 20on the power transmitter 1 while changing a size of each metallicobject. FIG. 7 shows a graph representing the characteristics of the Qvalues versus metal sizes (square sizes).

A measurement result using the iron (Fe) material and the aluminum (Al)material indicates that there may be a difference depending on ametallic material quality, although with an increase in a size of themetallic object 31, an effective resistance seems to increaseequivalently, leading to deterioration in the Q value. In other words,an increasing size of the metallic object is equivalent to the presenceof the metallic object in the vicinity of the power transmitting coil 6given the metallic object of the same size. The determination section23B compares the measured Q value (or a rate of change in the Q value)with a threshold stored on the memory 24 to determine whether or not themetallic object is present depending on whether or not the Q value iswithin a range of the threshold.

In such a manner, it is possible to detect the presence of a metallicobject in the vicinity of the power transmitting coil 6 based on ameasurement result of the Q value. The amount of deterioration in the Qvalue varies depending on a metallic material quality, and a metal witha greater degree of deterioration in the Q value may be easier togenerate heat. In other words, the Q value is related to a heatgenerating factor, and a metal to be detected that is likely to generateheat may be easier to be detected.

Next, the description is provided on measurement results of a Q value ina case where the power receiving coil 16 which is resonated with thepower transmitting coil 6 on the power transmitter 1, that is, the powerreceiver 11 is placed.

As shown in FIG. 8, as is the case with the metallic object 31, ameasurement was made in such a manner that the detecting circuit 20 wasoperated with the power receiver 11 brought close to the powertransmitter 1 that was mounted on the pedestal 30. Further, a coil usedas the power receiving coil 16 in this measurement is a spiral coil witha coil size of 30 mm (W1)*50 mm (W2) which has a structure similar tothat of the spiral coil illustrated in FIG. 6, and which is wound aroundusing the litz wire 41 with a wire diameter ϕ of 0.65 mm. As analternative to the magnetic material 42, a magnetic sheet made of aferrite material having a thickness of 0.2 mm is laid against a backsideof the spiral coil. An L value and a Q value of the power transmittingcoil 6 when the power receiver 11 is not present in the vicinity are14.0 μH and 48.4, respectively. A resonant frequency of the seriesresonant circuit including the power receiving coil 16 is 127.0 kHz. Thepower transmitting coil 6 on the power transmitter 1 is the same as thatillustrated in FIG. 6. A distance between the power transmitting coil 6and the power receiving coil 16 is fixed to 8 mm.

Variations in the Q values of the power transmitting coil 6 in changinga value of a resistance load that was connected with the series resonantcircuit on the power receiver 11 in such a state were measured using thedetecting circuit 20. FIG. 9 shows a graph representing thecharacteristics of a Q value of the resonant circuit on a powertransmitting side versus a load resistance of the resonant circuit on apower receiving side. In the figure, “open” denotes that the load sideof the series resonant circuit on the power receiver 11 is put in anopen state. Further, “no coil” denotes a state where no power receivingcoil 16 is connected.

It is seen from FIG. 9 that, with a decrease in the load resistance ofthe resonant circuit on the power receiving side, the Q value to bemeasured at the power transmitter 1 is on the decrease. Further, fromthe characteristic curve in FIG. 9, the same trend as above except for aslight variation amount was also found in a nonresonant coil as well(not shown in the figure). The determination section 23B compares themeasured Q value (or a rate of change in the Q value) with a thresholdstored on the memory 24 to determine whether or not a circuit includinga coil is present depending on whether or not the Q value is within arange of the threshold. In such a manner, it is possible to detect acircuit including a coil that may be electromagnetically coupled withthe power transmitting coil 6 by measuring the Q value of the seriesresonant circuit including the power transmitting coil 6.

Next, variations in the Q values at the time when a metallic object wasinterposed between the power transmitting coil 6 and the power receivingcoil 16 were measured in the same way.

FIG. 10 is a schematic cross-sectional view showing a state where ametallic object is interposed between the power transmitting coil 6 andthe power receiving coil 16. A metallic object 53 and a spacer 54 aredisposed between the power transmitting coil 6 with a magnetic material51 laid against the backside thereof and the power receiving coil 16with a magnetic sheet 52 attached against the backside thereof. In thismeasurement, when no metallic object is interposed, the Q value of theseries resonant circuit on the power transmitter 1 is 230.7, the Q valueof the series resonant circuit on the power receiver 11 is 48.4, acoupling factor k that is a degree of the electromagnetic couplingbetween the power transmitting coil 6 and the power receiving coil 16 is0.10, and an inter-coil efficiency is 0.83. A distance between the powertransmitting coil 6 and the power receiving coil 16 at this time is 8mm.

FIG. 11 shows measurement results obtained from the same circuit for theQ values of the series resonant circuits on the power transmitter 1(primary side) and the power receiver 11 (secondary side), the couplingfactor k, and the inter-coil efficiency at the time when the metallicobject 53 with a thickness of 1.0 mm is interposed.

A graph shown in FIG. 11 is represented with a rate of change where eachvalue at the time when the metallic object 53 is not interposed isnormalized as 100%. It is seen from this graph that the Q value of thesecondary-side coil has a greater rate of change as compared with a rateof change in the Q value of the primary-side coil, the coupling factor kand the inter-coil efficiency that may vary depending on a distancebetween coils or orientation of a coil. Accordingly, as compared withcurrently-available transmitting/receiving power efficiency methods, itis possible to detect a smaller metallic object that is interposedbetween the primary side (power transmitting coil 6) and the secondaryside (power receiving coil 16) by capturing variation in the Q value ofthe secondary-side coil. In other words, if the detecting circuit 20according to the present embodiment that detects the Q value is providedat the power receiver (secondary side), this makes it possible to detecta conductor and the like using only the power receiver, as well as toachieve higher detection sensitivity as compared with existing methods.For example, the determination section 23B compares the measured rate ofchange in the Q value for the secondary-side coil with a threshold (forexample, 90%) stored on the memory 24, and determines that a metallicobject is present between the primary-side coil and the secondary-sidecoil when the rate of change in the Q value is less than 90%, therebyallowing to detect such a metallic object.

Meanwhile, an inter-coil efficiency (ηrf) is obtained uniquely in theoryfrom a coupling factor k that is a degree of the electromagneticcoupling between a primary-side coil and a secondary-side coil, as wellas a primary-side Q value (Q1) and a secondary-side Q value (Q2) thatare each of Q values for a series resonant circuit with no load.Computational expressions to be used for obtaining the inter-coilefficiency (ηrf) are given in Expression (2) to Expression (4).

$\begin{matrix}{\eta_{rf} = \frac{S^{2}}{\left( {1 + \sqrt{1 + S^{2}}} \right)^{2}}} & \left\lbrack {{Math}.\mspace{14mu} 2} \right\rbrack \\{S = {kQ}} & \left\lbrack {{Math}.\mspace{14mu} 3} \right\rbrack \\{Q = \sqrt{Q_{1}Q_{2}}} & \left\lbrack {{Math}.\mspace{14mu} 4} \right\rbrack\end{matrix}$

In the present embodiment utilizing the electromagnetic coupling, eventhough the coupling factor k is low, Q values in the series resonantcircuits at the primary and secondary sides are set to high values,thereby enhancing a degree of freedom in arrangement of the primary-sidecoil and the secondary-side coil. As an example, a design is made toensure that the coupling factor k between the primary-side coil and thesecondary-side coil is 0.5 or less, and Q values of the primary-sidecoil or the secondary-side coil or both are 100 or more. The same istrue for second and third embodiments of the present disclosure to behereinafter described. As a matter of course, however, the presentembodiment is not limited to such a numerical value example.

(Advantageous Effects of First Embodiment)

According to the above-described first embodiment, a detecting circuit(detector) that is built in a primary side (power transmitter) or asecondary side (power receiver) determines a Q value or a degree ofvariation thereof in a circuit including a coil capable ofelectromagnetic coupling with an external object and performs detectionconcerning a state of the electromagnetic coupling with the externalobject based on a determined result. This makes it possible to detect aconductor (including a semiconductor) such as a metal, or a circuitincluding an electromagnetically coupled coil without the necessity fora combined use of a primary side (power transmitting side) and asecondary side (power receiving side). Accordingly, this allows aconductor or a circuit including a coil to be detected conveniently.

It is to be noted that, on the contrary, for example, in a method ofdetecting a metallic object based on information on an amplitude and aphase in the event of variation in the load of a power receiver(secondary side), or a method of detecting a metallic object fromvariation in the transmitting/receiving power efficiency, it isnecessary for detecting a metallic object to perform communication bycombined use of a power transmitter and a power receiver. In concreteterms, it may be also impossible to detect a metallic object in theevent that any signal arising between a metallic object other than apower receiving circuit and a proper power receiver for whichcommunication is disabled should be ridden on a coil of a powertransmitter.

Further, since a power transmitting coil or a power receiving coil thatis provided with a power transmitter or a power receiver, respectively,is used as a sensor, there is no necessity for providing any otherspecial sensors, which is quite advantageous from a viewpoint of spacesaving and cost saving. On the contrary, for example, in a method ofdetecting a metallic object by the use of a magnetic sensor, acapacitive sensor, an infrared sensor, or the like, it is necessary toarrange a sensor in a power transmitter and a power receiver in additionto the power transmitting coil or the power receiving coil. This adds arestriction in design to a device housing, which is also disadvantageousfrom a cost standpoint as well.

Additionally, unlike an inductance and a capacitance, a Q valuecorrelates with a heat generating factor, and thus a detecting circuit(detector) using the Q value according to the first embodiment is easyto detect any metal to be detected as much as possible that is likely togenerate heat.

What is more, as compared with existing circuits for detecting aconductor such as a metal, or a circuit including an electromagneticallycoupled coil in an inter-coil efficiency method, the present embodimentusing the Q value achieves higher detection sensitivity.

It is to be noted that, in the present embodiment, although thedescription is provided on a case of the magnetic field coupling (seeFIG. 1) as an example of the electromagnetic coupling, the electricfield coupling may be taken as an example. The magnetic field couplingand the electric field coupling exhibit the same behavior except foronly a difference that a coupling is based on an electric field or amagnetic field. In the case of the electric field coupling, this isallowed to be described as an equivalent circuit in a state where acapacitor on a power transmitter and a capacitor on a power receiver arearranged in opposition to each other. On this occasion, the Q value isobtained by measuring a voltage between a coil and a capacitor on aseries resonant circuit as a voltage V1 and by measuring a voltageacross the capacitor as a voltage V2.

2. Second Embodiment

In the first embodiment, the arithmetic processing section 23A obtains aQ value from the voltage V1 between the power transmitting coil and thecapacitor on the series resonant circuit and the voltage V2 across thepower transmitting coil, although in a second embodiment, the Q value isobtained in a half-value width method. In other words, in the arithmeticprocessing section 23A according to the second embodiment, the Q valuein a resonant circuit (series resonant circuit or parallel resonantcircuit) is obtained by using the half-value width method in theresonant circuit.

In the half-value width method, in the case where a series resonantcircuit is configured, as shown in FIG. 12, the Q value is obtained fromExpression (5) using a bandwidth (frequency range of f₁ to f₂) at whichimpedance of √2 times as much as an absolute value for impedance(Z_(peak)) at resonant frequency f₀ is achieved. In other words, in thiscase, the arithmetic processing section 23A obtains the Q value in theseries resonant circuit using the half-value width method based on theresonant frequency f₀ in the series resonant circuit and the frequencybandwidth (frequency range of f₁ to f₂) at which impedance of √2 timesas much as an absolute value for impedance at the resonant frequency f₀is achieved.

$\begin{matrix}{Q = \frac{f_{0}}{f_{2} - f_{1}}} & \left\lbrack {{Math}.\mspace{14mu} 5} \right\rbrack\end{matrix}$

Further, in the case where a parallel resonant circuit is configured, asshown in FIG. 13, the Q value is obtained from Expression (5) using abandwidth (frequency range of f₁ to f₂) at which impedance of (1/√2)times as much as an absolute value for impedance (Z_(peak)) at resonantfrequency f₀ is achieved. In other words, in this case, the arithmeticprocessing section 23A obtains the Q value in the parallel resonantcircuit using the half-value width method based on the resonantfrequency f₀ in the parallel resonant circuit and the frequencybandwidth (frequency range of f₁ to f₂) at which impedance of (1/√2)times as much as an absolute value for impedance at the resonantfrequency f₀ is achieved.

Also in the second embodiment where the Q value is determined in such amanner, it is possible to obtain the same advantageous effects as withthe first embodiment by virtue of the function similar to that in thefirst embodiment. It is to be noted that the second embodiment is alsoapplicable to both of the electric field coupling and the magnetic fieldcoupling that are mentioned in the first embodiment.

3. Third Embodiment

Unlike the first and second embodiments, a third embodiment representsan example where the arithmetic processing section 23A calculates the Qvalue from a ratio of a real part component to an imaginary partcomponent of impedance in a resonant circuit. In the present embodiment,a real part component and an imaginary part component of impedance aredetermined using an automatic balanced bridge circuit and a vector ratiodetector. In other words, the arithmetic processing section 23Aaccording to the second embodiment determines the real part componentand the imaginary part component of impedance in a resonant circuitusing the automatic balanced bridge circuit and the vector ratiodetector, and obtains the Q value in the resonant circuit from a ratioof the real part component to the imaginary part component.

FIG. 14 is a circuit diagram of an automatic balanced bridge forcalculating the Q value from a ratio of a real part component to animaginary part component of impedance according to the third embodiment.

An automatic balanced bridge circuit 60 shown in FIG. 14 is configuredin the same manner as a typically well-known inverting amplifiercircuit. A coil 62 is connected with an inverting input terminal(negative terminal) of an inverting amplifier 63, and a noninvertinginput terminal (positive terminal) is grounded. Subsequently, using afeedback resistor element 64, a negative feedback is applied from anoutput terminal to the inverting input terminal (negative terminal) ofthe inverting amplifier 63. Further, an output (voltage V1) of analternating-current power supply 61 for inputting an alternating-currentsignal to the coil 62 and an output (voltage V2) of the invertingamplifier 63 are input to a vector ratio detector 65. The coil 62corresponds to the power transmitting coil 6 or the power receiving coil16 in FIG. 1.

The automatic balanced bridge circuit 60 operates in such a manner thata voltage on the inverting input terminal (negative terminal) becomeszero at ant time by a negative feedback action. Further, a currentflowing from the alternating-current power supply 61 to the coil 62flows into the feedback resistor element 64 in almost all cases becauseof a large input impedance of the inverting amplifier 63. As a result, avoltage across the coil 62 becomes equal to the voltage V1 of thealternating-current power supply 61, and an output voltage of theinverting amplifier 63 becomes a product of a current I flowing throughthe coil 62 and a feedback resistance Rs. The feedback resistance Rs isa given reference resistance. Therefore, if a ratio of the voltage V1 tothe voltage V2 is determined by detecting those voltages, impedance isobtained. Since the vector ratio detector 65 determines the voltage V1and the voltage V2 as a complex number, information on a phase of thealternating-current power supply 61 (denoted by a dashed line) isutilized.

In the present embodiment, by the use of such an automatic balancedbridge circuit 60, such a vector ratio detector 65, and the like, a realpart component R_(L) and an imaginary part component X_(L) of impedanceZ_(L) in a resonant circuit is determined, and the Q value is obtainedfrom a ratio of R_(L) to X_(L). Expression (6) and Expression (7) asgiven below are computational expressions representing a process fordetermining the Q value.

$\begin{matrix}{Z_{L} = {{R_{L} + {j\; X_{L}}} = {\frac{V\; 1}{I} = {\frac{V\; 1}{V\; 2}{Rs}}}}} & \left\lbrack {{Math}.\mspace{14mu} 6} \right\rbrack \\{Q = \frac{X_{L}}{R_{L}}} & \left\lbrack {{Math}.\mspace{14mu} 7} \right\rbrack\end{matrix}$

Also in the third embodiment where the Q value is determined in such amanner, it is possible to obtain the same advantageous effects as withthe first and second embodiments by virtue of the function similar tothat in the first and second embodiments. It is to be noted that thethird embodiment is also applicable to both of the electric fieldcoupling and the magnetic field coupling that are mentioned in the firstembodiment.

4. Others

It is to be noted that, in the above-described first to thirdembodiments of the present disclosure, although a Q value at a resonantfrequency is measured, a frequency at which the Q value is measured doesnot necessarily have to coincide with the resonant frequency providedthat a slight deterioration in the detection sensitivity is allowable,and the Q value that is measured at a frequency shifted from theresonant frequency may be used.

Further, when a conductor such as a metal, or a circuit including a coilcomes close to a primary-side coil or a secondary-side coil, althoughnot only a Q value but also an L value (inductance value of coil) variesto cause a resonant frequency to be shifted, a state of theelectromagnetic coupling may be detected by the combined use of aresonant frequency shift that is caused by variation in the L value aswell as the Q value. In other words, a detecting section may performdetection concerning a state of the electromagnetic coupling with anexternal object by the combined use of the Q value in a resonant circuitand the L value in the resonant circuit.

Additionally, when a metallic object is interposed between a powertransmitting coil and a power receiving coil, although a coupling factork also varies, combined use of variations in a value of the couplingfactor k and a Q value may be permitted for determination of a state ofthe electromagnetic coupling. In other words, a detecting section mayperform detection concerning a state of the electromagnetic couplingwith an external object by the combined use of the Q value in a resonantcircuit and a value of the coupling factor k in the event of theelectromagnetic coupling.

Furthermore, as the power transmitting coil and the power receiving coilaccording to the respective embodiments of the present disclosure,although the description is provided on an example of a coil having nocore, any coil of a structure of being wound around a core having amagnetic material may be employed alternatively.

In addition, although a series of processes in the above-describedrespective embodiments of the present disclosure is executable inhardware, this is also executable in software. When such a series ofprocesses is executed in software, this is executable using a computer(MPU and the like) in which any program configuring the software isbuilt into a dedicated hardware, or a computer with installed programsfor executing various functions.

What is more, processing steps describing time-series processes in thepresent specification include processes to be performed in parallel orindividually (for example, parallel processing or object-orientedprocessing) even though they are not necessarily processed inchronological order, in addition to processes to be performed in atime-series manner in order of description as a matter of course.

It is to be noted that the present technology may be also configured asfollows.

-   (1) A detector including

a detecting section determining a Q value or a degree of variation ofthe Q value in a circuit including a coil capable of electromagneticcoupling with an external object and performing detection concerning astate of the electromagnetic coupling with the external object based ona determined result.

-   (2) The detector according to (1), wherein the detecting section    detects whether a conductor or another circuit including another    coil is present in the vicinity of the coil as the state of the    electromagnetic coupling with the external object.-   (3) The detector according to (2), wherein when the presence of the    conductor or the another circuit in the vicinity of the coil is    detected, the detecting section further detects whether the detected    object is one of the conductor and the another circuit.-   (4) The detector according to (3), wherein the detecting section    detects whether the detected object is one of the conductor or the    another circuit based on a result of determining whether    communication with the external object via the coil is possible.-   (5) The detector according to (4), wherein the detecting section    decides that the detected object is the another circuit when it is    determined that the communication with the external object is    possible, and decides that the detected object is the conductor when    it is determined that the communication with the external object is    not possible.-   (6) The detector according to (4) or (5), further including a    communication control section controlling the communication with the    external object, wherein

when the presence of the conductor or the another circuit in thevicinity of the coil is detected, the detecting section instructs thecommunication control section to output a transmission signal to thedetected object and determines whether the communication with theexternal object is possible depending on the presence or absence of aresponse to the transmission signal.

-   (7) The detector according to (6), wherein the detecting section    determines that the communication with the external object is    possible when there is a response to the transmission signal, and    determines that the communication with the external object is not    possible when there is no response to the transmission signal.-   (8) The detector according to any one of (1) to (7), wherein the    detecting section includes:

an arithmetic processing section calculating the Q value or a degree ofvariation of the Q value; and

a determination section determining a state of the electromagneticcoupling with the external object by comparing the Q value or a degreeof variation of the Q value that is calculated by the arithmeticprocessing section with a predetermined threshold.

-   (9) The detector according to (8), wherein the circuit is a resonant    circuit including the coil and a capacitor, and

the arithmetic processing section calculates the Q value in the resonantcircuit from a ratio of a first voltage that is a voltage between thecoil and the capacitor in the resonant circuit to a second voltage thatis a voltage across the coil in the resonant circuit.

-   (10) The detector according to (8), wherein the circuit is a    resonant circuit including the coil and a capacitor, and

the arithmetic processing section calculates the Q value in the resonantcircuit by using a half-value width method in the resonant circuit.

-   (11) The detector according to (10), wherein the resonant circuit is    a series resonant circuit, and

the arithmetic processing section calculates the Q value in the seriesresonant circuit using the half-value width method based on a resonantfrequency in the series resonant circuit and a bandwidth frequency atwhich impedance of √2 times as much as an absolute value for impedanceat the resonant frequency is achieved.

-   (12) The detector according to (10), wherein the resonant circuit is    a parallel resonant circuit, and

the arithmetic processing section calculates the Q value in the parallelresonant circuit using the half-value width method based on a resonantfrequency in the parallel resonant circuit and a bandwidth frequency atwhich impedance of (1/√2) times as much as an absolute value forimpedance at the resonant frequency is achieved.

-   (13) The detector according to (8), wherein the circuit is a    resonant circuit including the coil and a capacitor, and

the arithmetic processing section determines a real part component andan imaginary part component of impedance in the resonant circuit usingan automatic balanced bridge circuit and a vector ratio detector, andcalculates the Q value in the resonant circuit from a ratio of the realpart component to the imaginary part component.

-   (14) The detector according to any one of (8) to (13), wherein the    threshold corresponds to a Q value in the circuit under a condition    that the conductor and the another circuit are not present in the    vicinity of the coil.-   (15) The detector according to any one of (1) to (14), wherein the    detecting section performs detection concerning a state of the    electromagnetic coupling with the external object by the combined    use of the Q value in the circuit and one of an L value in the    circuit and a value of a coupling factor k in the event of the    electromagnetic coupling.-   (16) A power transmitter, including:

a power transmitting coil capable of electromagnetic coupling with anexternal object;

a power transmitting section performing power transmission using thepower transmitting coil; and

a detecting section determining a Q value or a degree of variation ofthe Q value in a circuit including the power transmitting coil andperforming detection concerning a state of the electromagnetic couplingwith the external object based on a determined result.

-   (17) A power receiver, including:

a power receiving coil capable of electromagnetic coupling with anexternal object;

a power receiving section performing power reception using the powerreceiving coil; and

a detecting section determining a Q value or a degree of variation ofthe Q value in a circuit including the power receiving coil andperforming detection concerning a state of the electromagnetic couplingwith the external object based on a determined result.

-   (18) A power feed system, including:

one or a plurality of power receivers; and

one or a plurality of power transmitters performing power transmissionutilizing the electromagnetic coupling for the power receivers, wherein

the power transmitter has a power transmitting coil capable ofelectromagnetic coupling with an external object, and a powertransmitting section performing power transmission using the powertransmitting coil,

the power receiver has a power receiving coil capable of electromagneticcoupling with an external object, and a power receiving sectionperforming power reception using the power receiving coil, and

a detecting section determining a Q value or a degree of variation ofthe Q value in a circuit including one of the power transmitting coiland the power receiving coil and performing detection concerning a stateof the electromagnetic coupling with the external object based on adetermined result is provided one or both of the power transmitter andthe power receiver.

-   (19) The power feed system according to (18), wherein the detecting    section is provided in the power receiver.-   (20) A detection method, including:

a first step of determining a Q value or a degree of variation of the Qvalue in a circuit including a coil capable of electromagnetic couplingwith an external object; and

a second step of performing detection concerning a state of theelectromagnetic coupling with the external object based on a resultdetermined in the first step.

The present disclosure is not limited to the above-described respectiveembodiments, but any other various modification examples and applicationexamples are available as a matter of course insofar as they are withinthe scope of the appended claims or the equivalents thereof.

The present application contains subject matter related to thatdisclosed in Japanese Priority Patent Application JP 2011-081018 filedin the Japan Patent Office on Mar. 31, 2011, the entire content of whichis hereby incorporated by reference.

The invention claimed is:
 1. A detector comprising a detecting circuitconfigured to determine a value of a Q factor or a degree of variationof the value of the Q factor in a first circuit including a first coilconfigured to electromagnetically couple with an external object, and todetect whether the external object is present in the vicinity of thefirst coil; determination circuitry configured to determine, in a casewhere the detecting circuit detects that the external object is presentin the vicinity of the first coil, whether the external object is asecond circuit including a second coil or is another conductor based ona comparison of the determined value of the Q factor or the determineddegree of variation of the value of the Q factor with a predeterminedthreshold, and configured to generate a control signal indicating aresult of the determination; and communication control circuitryconfigured to selectively begin a non-contact power transmission to theexternal object in response to the control signal, wherein the value ofthe Q factor or the degree of variation of the value of the Q factor isdetermined based on a ratio of voltages or an impedance, and wherein thepredetermined threshold corresponds to a value of the Q factor in thefirst circuit under a condition that neither the other conductor nor thesecond circuit are present in the vicinity of the first coil.
 2. Thedetector according to claim 1, wherein the detecting circuit isconfigured to detect whether the external object is present in thevicinity of the first coil using a state of the electromagnetic couplingwith the external object.
 3. The detector according to claim 2, whereinthe determination circuitry is configured to determine whether theexternal object is the other conductor or the second circuit based on aresult of determining whether communication with the external object viathe first coil is possible.
 4. The detector according to claim 3,wherein the determination circuitry is configured to decide that theexternal object is the second circuit when it is determined that thecommunication with the external object is possible, and to decide thatthe external object is the other conductor when it is determined thatthe communication with the external object is not possible.
 5. Thedetector according to claim 3, wherein in a case where the presence ofthe external object in the vicinity of the first coil is detected, thedetecting circuit is configured to instruct the communication controlcircuitry to output a transmission signal to the external object and todetermine whether the communication with the external object is possibledepending on the presence or absence of a response to the transmissionsignal.
 6. The detector according to claim 5, wherein the detectingcircuit is configured to determine that the communication with theexternal object is possible when there is a response to the transmissionsignal, and to determine that the communication with the external objectis not possible when there is no response to the transmission signal. 7.The detector according to claim 1, wherein the detecting circuitincludes: arithmetic processing circuitry configured to calculate thevalue of the Q factor or the degree of variation of the value of the Qfactor; and the determination circuitry, the determination circuitrybeing further configured to determine a state of the electromagneticcoupling with the external object by comparing the value of the Q factoror the degree of variation of the value of the Q factor that iscalculated by the arithmetic processing a circuitry with thepredetermined threshold.
 8. The detector according to claim 7, whereinthe first circuit is a resonant circuit including the first coil and acapacitor, and the arithmetic processing circuitry is configured tocalculate the value of the Q factor in the resonant circuit from a ratioof a first voltage between the first coil and the capacitor in theresonant circuit to a second voltage across the first coil in theresonant circuit.
 9. The detector according to claim 7, wherein thefirst circuit is a resonant circuit including the first coil and acapacitor, and the arithmetic processing circuitry is configured tocalculate the value of the Q factor in the resonant circuit by using ahalf-value width method in the resonant circuit.
 10. The detectoraccording to claim 9, wherein the resonant circuit is a series resonantcircuit, and the arithmetic processing circuitry is configured tocalculate the value of the Q factor in the series resonant circuit usingthe half-value width method based on a resonant frequency in the seriesresonant circuit and a bandwidth frequency at which an impedance of √2times as much as an absolute value for an impedance at the resonantfrequency is achieved.
 11. The detector according to claim 9, whereinthe resonant circuit is a parallel resonant circuit, and the arithmeticprocessing circuitry is configured to calculate the value of the Qfactor in the parallel resonant circuit using the half-value widthmethod based on a resonant frequency in the parallel resonant circuitand a bandwidth frequency at which an impedance of (1/√2) times as muchas an absolute value for an impedance at the resonant frequency isachieved.
 12. The detector according to claim 7, wherein the firstcircuit is a resonant circuit including the first coil and a capacitor,and the arithmetic processing circuitry is configured to determine areal part component and an imaginary part component of an impedance inthe resonant circuit using an automatic balanced bridge circuit and avector ratio detector, and to calculate the value of the Q factor in theresonant circuit from a ratio of the real part component to theimaginary part component.
 13. The detector according to claim 1, whereinthe detecting circuit is configured to perform detection concerning astate of the electromagnetic coupling with the external object by thecombined use of the value of the Q factor in the circuit and one of an Lvalue in the circuit and a value of a coupling factor k in the event ofthe electromagnetic coupling.
 14. A power transmitter, comprising: apower transmitting coil configured to electromagnetically couple with anexternal object; a power transmitting section configured to performpower transmission using the power transmitting coil; a detectingcircuit configured to determine a value of a Q factor or a degree ofvariation of the value of the Q factor in a first circuit including thepower transmitting coil, and to detect whether the external object ispresent in the vicinity of the power transmitting coil; determinationcircuitry configured to determine, in a case where the detecting circuitdetects that the external object is present in the vicinity of the firstpower transmitting coil, whether the external object is a second circuitincluding a second coil or is another conductor based on a comparison ofthe determined value of the Q factor or the determined degree ofvariation of the value of the Q factor with a predetermined threshold,and configured to generate a control signal indicating a result of thedetermination; and communication control circuitry configured toselectively begin a non-contact power transmission to the externalobject in response to the control signal, wherein the value of the Qfactor or the degree of variation of the value of the Q factor isdetermined based on a ratio of voltages or an impedance, and wherein thepredetermined threshold corresponds to a value of the Q factor in thefirst circuit under a condition that neither the other conductor nor thesecond circuit are present in the vicinity of the power transmittingcoil.
 15. A power receiver, comprising: a power receiving coilconfigured to electromagnetically couple with an external object; apower receiving section configured to perform power reception using thepower receiving coil; a detecting circuit configured to determine avalue of a Q factor or a degree of variation of the value of the Qfactor in a first circuit including the power receiving coil, and todetect whether the external object is present in the vicinity of thepower receiving coil; determination circuitry configured to determine,in a case where the detecting circuit detects that the external objectis present in the vicinity of the first power receiving coil, whetherthe external object is a second circuit including a second coil or isanother conductor based on a comparison of the determined value of the Qfactor or the determined degree of variation of the value of the Qfactor with a predetermined threshold, and configured to generate acontrol signal indicating a result of the determination; andcommunication control circuitry configured to selectively begin anon-contact power reception from the external object in response to thecontrol signal, wherein the value of the Q factor or the degree ofvariation of the value of the Q factor is determined based on a ratio ofvoltages or an impedance, and wherein the predetermined thresholdcorresponds to a value of the Q factor in the first circuit under acondition that neither the other conductor nor the second circuit arepresent in the vicinity of the power receiving coil.
 16. A power feedsystem, comprising: one or a plurality of power receivers; and one or aplurality of power transmitters configured to perform power transmissionutilizing an electromagnetic coupling with the power receivers, whereina respective power transmitter has a power transmitting coil configuredto electromagnetically couple with an external object, and a powertransmitting section configured to perform power transmission using thepower transmitting coil, a respective power receiver has a powerreceiving coil configured to electromagnetically couple with theexternal object, and a power receiving section configured to performpower reception using the power receiving coil, a respective powertransmitter or a respective power receiver includes: a detecting circuitconfigured to determine a value of a Q factor or a degree of variationof the value of the Q factor in a first circuit including one of thepower transmitting coil and the power receiving coil, and to detectwhether the external object is present in the vicinity of the powertransmitting coil or the power receiving coil; determination circuitryconfigured to determine, in a case where the detecting circuit detectsthat the external object is present in the vicinity of the powertransmitting coil or the power receiving coil, whether the externalobject is a second circuit including a second coil or is anotherconductor based on a comparison of the determined value of the Q factoror the determined degree of variation of the value of the Q factor witha predetermined threshold, and configured to generate a control signalindicating a result of the determination; and communication controlcircuitry configured to selectively begin a non-contact power transferwith the external object in response to the control signal, the value ofthe Q factor or the degree of variation of the value of the Q factor isdetermined based on a ratio of voltages or an impedance, and thepredetermined threshold corresponds to a value of the Q factor in thefirst circuit under a condition that neither the other conductor nor thesecond circuit are present in the vicinity of the power transmittingcoil or the power receiving coil.
 17. The power feed system according toclaim 16, wherein the detecting circuit is provided in the respectivepower receiver.
 18. A detection method, comprising: determining a valueof a Q factor or a degree of variation of the value of the Q factor in afirst circuit including a first coil configured to electromagneticallycouple with an external object; and detecting whether the externalobject is present in the vicinity of the first coil; determining, in acase where the external object is present in the vicinity of the firstcoil, whether the external object is a second circuit including a secondcoil or is another conductor based on a comparison between thedetermined value of the Q factor or the determined degree of variationof the value of the Q factor; generating a control signal indicating aresult of the determining whether the external object is the secondcircuit or the other conductor; and selectively beginning a non-contactpower transmission to the external object in response to the controlsignal, wherein the Q value or the degree of variation of the Q value isdetermined based on a ratio of voltages or an impedance, and wherein thepredetermined threshold corresponds to a value of the Q factor in thefirst circuit under a condition that neither the other conductor nor thesecond circuit are present in the vicinity of the first coil.
 19. Thedetector according to claim 1, wherein the predetermined threshold isdetermined before the detecting circuit detects whether the externalobject is present in the vicinity of the first coil.